Does an agreement to purchase a jet ski and operate it through a person who owns a jet ski rental business, in exchange for a specified percentage of the revenue, constitute usury (riba)?

There is no objection to buying a bicycle from a person and leaving it with him for him to rent out to customers for a known fee that you pay him. It is not permissible for the fee to be a percentage of what he earns; rather, it must be a known amount. If the buyer stipulates to the seller, at the time of sale, that he maintain and rent it out, then this condition is valid if the benefit is known.